Bacteria in nodules attached to the roots of certain plants perform nitrogen fixation, converting atmospheric nitrogen into ammonia, which plants can use. This process is distinct from other nitrogen transformations like denitrification, ammonification, and nitrification. Therefore, the correct answer to the question is D. nitrogen fixation .
;
Bacteria in nodules on certain plants, specifically legumes, perform nitrogen fixation, converting atmospheric nitrogen into a usable form for plants. This process allows plants to thrive by increasing soil nitrogen levels, essential for plant growth. It is distinct from other nitrogen-related processes such as denitrification, ammonification, and nitrification. ;